Fertile Heifers. Target

Transcription

1 Setting appropriate rearing targets for two-year calving Monitoring growth rates and body condition Managing the first service and herd entry. Objective: To rear heifers to enter the herd at the correct weight and age for the best production and fertility performance. Challenge: Establish clear targets for your heifer rearing and monitor performance closely over the rearing period. Fertile Heifers Ensure your heifers are served effectively and introduced into the milking herd carefully. The economic value of rearing heifers to calve into the herd at two rather than the traditional three years of age has been well-established. For Holstein-Friesian heifers weighing kg post-calving this requires challenging but perfectly achievable average liveweight gains of over 0.7kg/day from birth to calving. Other breeds with lower mature body weights require lower rates of daily gain. The way heifers are reared and managed to meet the two-year calving target and then introduced into the milking herd is clearly important in maximising fertility as well as production capacity. Target Calve heifers at two years of age with optimum fertility Rearing Costs Page 10-1 Growth Targets Page 10-2 Rearing Practice Page 10-4 Service Options Page 10-7 Herd Introduction Page :10/07 10

2 Action Plan To calve your heifers at two years of age with optimum fertility Review Your Rearing Costs Assess your current heifer rearing costs and explore ways of reducing them by changing your herd replacement policy Set Clear Rearing Targets Establish realistic growth targets for your particular system and assess withers height regularly to monitor performance against them Feed Sufficient Colostrum Ensure all your heifer calves receive sufficient high quality colostrum soon enough after birth to give them the greatest immunity to infection Manage Your Calf Rearing Manage your calves on an accelerated growth system to take full advantage of their superior feed conversion efficiency and early growth potential Get Your Heifer Feeding Right Feed your heifers up to first service and through pregnancy to meet your particular growth targets without becoming too fat Manage Natural Service Check the fertility of any natural service sire you use on heifers in advance and employ controlled breeding techniques if necessary Manage Herd Introduction Minimise the stress you place on your heifers as they enter the herd through careful stock management. Page 10-1 Page 10-2 Page 10-4 Page 10-4 Page 10-5 Page 10-7 Page :10/07 10

3 Rearing Costs Heifer rearing is a significant cost for most dairy herds. With replacement rates of up to 40% (2.5 lactations average herd life) in some herds it is taking as long to rear a heifer as she eventually spends in the herd. Age at calving and herd culling rate both have a large effect on the number of replacements needed and the cost being carried (Table 10.1). Table 10.1: Total Number of Heifers Needed by a 100 Cow Herd at Different Culling Rates and Ages at First Calving. Age at First Calving (months) Herd Culling Rate (%) assuming 5% calf mortality A 100-cow herd with a culling rate of 23% calving heifers at 24 months of age needs to carry 16 less replacements of all ages than one with a culling rate of 26% calving at 28 months. Age at calving does not have a major effect on the direct cost of rearing. However, when the amount of milk produced to 30 months of age is taken into account at a margin over all feed and quota costs of 10p/litre, the net effect on cash flow of rearing a heifer to 30 months is much less for the heifers which calve earlier (Table 10.2). Table 10.2: Cost of Rearing Heifers to Calve at Different Ages. Age at Calving Cost of Rearing to Calving * Milk from Calving to 30 months ** Margin Over All Feed & Quota *** Net Cost to 30 Months (months) ( ) (litres) ( ) ( ) * Including variable costs, labour and finance but not machinery or building depreciation, electricity and water. ** at 25 litres/day. *** at 10p/litre. Even if an allowance is made for the lower yield for younger-calving heifers early calving is still advantageous. Earlier calving, of course, also lowers costs by reducing the number of heifers that have to be carried at any one time (Table 10.1). Alternatives to home rearing include contracting-out heifer rearing or maintaining a flying herd, with all replacements bought as close to calving or calved heifers. The value of contract rearing will depend on the professionalism of the rearer and the charges levied. Equally, if a flying herd policy is followed, the calf sale (plus interest on the money less rearing costs to one week old) can be used to offset the purchase price of a replacement. This approach is very exposed to market price fluctuations for replacement stock and creates significant biosecurity problems. However, it does enable low or moderate genetic merit herds to improve faster than would be possible by breeding-up. Because heifer rearing can be a significant drain on resources, each herd needs to examine its current replacement policy and realistic alternatives carefully for best overall business value. In particular, the costs of the capital tied-up in rearing heifers need to be appreciated. Fact Sheet 12 assesses the suitability of different herd replacement systems 3:10/

4 Growth Targets Research has established that heifer weight rather than age determines when puberty occurs and oestrus cycling begins. The first signs of heat usually appear when heifers have reached about 40% of their mature body weight. While sexual maturity occurs at just under 12 months of age in well-fed heifers, under-feeding and other stress-inducing conditions can delay the onset of cycling. Contrary to conventional wisdom suggesting milk production may be reduced by growing heifers above kg/day, current work suggests no harm done will be done by growing Holstein dairy replacements at up to or just over 1kg/day for at least some of their rearing period. Provided the high rate of growth does not lead to excessive body condition which could do permanent damage persisting to calving there appears to be little need for a period of slow growth prior to puberty. Individual herd mature weights can be checked by weighing third and fourth calvers or by monitoring the weights of cull cows leaving the farm, provided they are around Body Condition Score 3.0. While heifer targets have traditionally been set in terms of liveweight, these can result in small fat animals being served too early. Frame size assessed by height at the withers is perhaps the most valuable measure of heifer growth. Apart from being a more meaningful indicator of heifer development, height at the withers is very much easier to measure than liveweight. It can be done with a yardstick while animals are in the crush or estimated by walking heifers alongside a wall with the target line clearly marked. Around 75% of frame growth typically occurs pre-puberty, with growth levelling off as animals approach two years of age (Figure 10.1). Figure 10.1: Typical Dairy Heifer Frame Growth Curve. The key to successful heifer rearing for two year calving is to maximise weight gains without creating over-fat animals. Setting Rearing Targets Research and experience confirm that heifer growth targets are best set as a percentage of mature weight and size within both breed and herd (Table 10.3). Table 10.3: Heifer Growth Targets Age/stage Percentage of mature weight (%) 6 months 30 9 months 40 Mating Pre-calving 90 Post-calving 85 Second calving 92 Weight-for-age and frame growth curves can be used to set detailed rearing targets for the main dairy breeds (Table 10.4) :10/07

5 Table 10.4 Heifer Rearing Targets for the Main Dairy Breeds Age (months) Weight (kg) Holstein Friesian Jersey Withers height (cm) Weight (kg) Withers height (cm) Weight (kg) Withers height (cm) (mating) (pre-calving) (post-calving) For other breeds or crosses target weight-for-age guidelines should be set on the basis of percentage of mature bodyweight (Table 10.3) or withers height-for-age (Table 10.5) Table 10.5: Withers Height-for-Age Targets for Other Breeds Age Target Withers Height (cm) (months) Ayrshire Brown Swiss Shorthorn :10/

6 Rearing Practice To achieve the most rapid growth without over-fatness for the optimum financial and reproductive efficiency requires careful heifer management from birth to first calving and beyond. It is important to monitor heifer performance regularly over the rearing period to achieve the required targets, using withers height as a good measure and undertaking Body Condition Scoring (Section 7). Feeding Colostrum The first essential in heifer rearing is to ensure all calves receive sufficient colostrum early enough. As a general rule, calves should have at least 10% of their bodyweight as colostrum in the first 24 hours of life, ideally half of this within six hours of birth. If Johne s disease is present in the herd, calves should only be fed colostrum from their own mothers or artificial colostrum substitutes to minimise the risk of spread. Providing the herd is clear of Johne s disease, feeding pooled colostrum can help by bathing the lining of the gut with surface-active immunoglobulins against rotavirus amongst other infections. The use of pasteurisers for colostrum is worth considering on large units. Managing Calf Rearing Feeding a 10% solution of milk powder at 10% of the calf s bodyweight to standard UK practice will produce healthy calves. However, it will also seriously restrict growth rates at the time of the highest potential feed conversion efficiency in the animal s life. Accelerated calf growth systems, feeding as high a level of high protein milk replacer as calves can safely utilise, have been shown in US practice to give much heavier heifers at weaning and better development of udder secretory tissue. If possible the colostrum should be sucked from a teat (cow or bottle) as this by-passes the rumen for more rapid absorption. Calves need to suckle continuously for minutes to take two litres of colostrum. It is important to make the best use of the strong suckling drive calves appear to have in the first hour or two of life before it wanes. Calves that will not suck the cow or a bottle teat will require a stomach tube but this delays absorption by putting the colostrum into the rumen. When the gut is open to absorb antibodies, of course, it is highly susceptible to bacterial infection, making feeding hygiene in the first 24 hours more important than at any other time of life. Bacterial numbers in warm colostrum in a bucket can double every 20 minutes. It is important to appreciate, however, that an accelerated calf growth system means heifers have to be calved at two years of age or younger to recoup the costs. High protein (26-28%) low fat (15-16%) milk powders are essential for accelerated calf growth systems. These contrast with normal 22-23% protein, 19-20% fat powders. Feed rates and mixing rates are also increased from the normal 10% to around 15%. With a feed conversion efficiency of 1.25:1 at best, powder intakes of 900g/day are needed for maximum growth rates (0.7kg/day+). Calves will be slightly looser on these high milk replacer intakes but any scouring will not be caused by the high feeding level :10/07

7 Providing calf health status is good the system of milk feeding has been shown to make very little difference to growth rates, the weight of milk solids consumed being the determining factor. Given that the labour needed for twice daily bucket feeding is almost six times more than that required for ad lib machine feeding or group feeding from a barrel, these alternatives offer valuable opportunities for time and cost saving. Concentrate Feeding Good feeding and management must be maintained through weaning and beyond if excellent calves at eight weeks of age are not to end up at a similar weight and size to more traditionally grown animals at 12 weeks at a very much higher cost. Grain has been shown to be more effective than forage in the very early development of the rumen, leading to significant rumen lining development by four weeks of age and reduced nutritional stress at weaning. Concentrates should, consequently, be made available from a few days of age. Where rapid calf growth is required there may be a value in increasing the protein content in the calf starter concentrates above the 18% which has been shown to be optimal under conventional rearing systems. High digestible undegradable (by-pass) protein sources do not appear to offer any advantage, soya being quite suitable. On high input systems, higher protein concentrates may help in achieving bigger rather than just fatter calves. However, the first essential is to ensure the concentrate is sufficiently palatable so calves will actually consume it at the right level to support their development. Ventilation The health status of heifers has to be high to ensure efficient feed conversion and fast growth rates. In particular, housing must be well-ventilated to avoid respiratory problems. If better accommodation is not available, forced ventilation should be considered where old poorly ventilated buildings are used. While air flow must be maximised, it is equally important to avoid draughts. Sharing air space with older cattle should also be avoided. Calf hutches for individuals or small groups of calves provide an optimum environment but can be labour intensive. Feeding to First Service From weaning to kg (for Holsteins) the rate of weight gain greatly influences the age at which heifers first come into oestrus. Puberty, related primarily to body weight, can be reached at any time from eight months to 16 months of age under commercial farm conditions. Since fertility increases up to the third oestrus cycle after puberty, heifers need to be grown to reach puberty at least six weeks before the start of serving. To ensure successful implantation of the embryo a generous level of feeding should continue for six weeks after service. Recent studies show that growing heifers faster does not lead to a reduction in the rate of daily development of secretory tissue in the udder. While milk yields may be lower when heifers calve younger, this is now considered to be due to age alone, not rate of growth. A high number of secretory cells does not guarantee higher milk yields but could increase potential yields. Likely yield reductions in the first lactation with age at first calving are difficult to predict with any accuracy but can be estimated (Table 10.6). 3:10/

8 Table 10.6: Estimated First Lactation Yield by Age at First Calving Age at First Lactation Yield First Calving Compared to 24 Month Calving (months) (%) Limited investigations with periods of restricted growth followed by periods of generous feeding have shown heifer lactation yields may be improved by 8-21% through a step-feeding approach. Since step-feeding is difficult to manage accurately in commercial practice, the main value of this work is in confirming that below target performance earlier in the rearing period can be overcome by increased feeding in the later stages without damaging future performance. Care must, however, be taken in pushing heifer growth rates post-puberty because this tends to increase body condition rather than frame size. Feeding During First Pregnancy Although there is little scope to increase frame size at this late stage in heifer development, severe underfeeding could still prevent animals achieving the small potential which does exist. Growth rates of kg/day are recommended during the first pregnancy to achieve a Condition Score of 3.0 at calving, the key being to avoid heifers getting over-fat. Step-feeding work suggests there may be a benefit in growing heifers at less than 0.8kg for part of pregnancy and boosting this in the last 3 months. However, high weight gains from concentrate feeding in late pregnancy can result in excess condition at calving which must be avoided if fertility is not to be compromised (Section 7). Heifers will not suffer from milk fever, and there is evidence that anionic salts like magnesium chloride will depress feed intake more in heifers than in cows. Wherever possible, therefore, heifers should be kept separate from cows in the last few weeks of pregnancy so they do not receive anionic salts. Udder oedema can be a problem in heifers, particularly if they calve on high protein, high potash pastures or are receiving diets containing a high proportion of grass silage. Feeding mature forages or diets high in whole crop or maize silage will reduce this danger. Managing to Reduce Lameness It has been suggested that nutrition during the rearing period may have an important effect on claw development, and the sole ulcers and white line lesions that cause the most damaging lameness. Given the major impact of lameness on both heat expression and detection (Section 6) and Pregnancy Rates (Section 8), careful management of rearing rations may make a valuable additional contribution to fertility improvement. To minimise lameness problems, heifers should be: Fed dry diets (over 30% DM silage) where possible Kept off straw beds in summer housing Trained to use cubicles when bulling or in-calf Allowed to remain in straw yards for 8 weeks after calving. Over-fatness is unlikely to be a problem unless high levels of concentrates are fed or heifers will be calving at more than 2 1 / 4 years old :10/07

9 Service Options Running a bull with heifers offers well-recognised Heat Detection and Pregnancy Rate benefits, particularly in groups of animals reared away from the main unit and not handled or seen as regularly as the milking herd. The choice of bull should take into account size, calving issues, calf value and the housing, handling and grazing conditions under which the cattle are kept. Fact Sheet 10 gives practical advice on calving difficulties and how to avoid them Unlike mature cows, the use of prostaglandin treatment with heifers has no negative impact on Pregnancy Rates and, on occasion, may even have a positive effect. Herd Introduction Grouping dairy heifers with mature cows soon after calving often results in stress which can seriously affect fertility performance (Section 6). A bull fertility check is an essential investment in view of the numerous cases of infertile bulls running with heifers and resulting in the late calving of a whole year s replacements, seriously compromising the calving pattern Ideally, change bulls weekly giving each one week working followed by one week resting to avoid the danger of impairing fertility by over-working. Controlled breeding and synchronisation (Section 8) can bring particular benefits for heifers. Most notably: Giving better control of their entry into the herd Tightening the calving pattern Allowing AI to be used more effectively, and easy-calving bulls to be selected Speeding-up the rate of genetic improvement by enabling dairy semen to be used. An MDC-sponsored project presents the following guidelines for heifer management to reduce this stress: Where possible, heifers should be kept as a separate milking group for at least the first four months of the lactation promoting fair competition at the feed trough and allowing them to continue growing, so they reach their peak yield and get back into calf before having to compete with older animals If they are to be managed as part of a cow group, heifers need to be well-grown and the facilities must provide adequate lying space for the whole herd Heifers should always be kept in a recently calved group and not mixed with the herd until at least five days after calving Initial introduction into the herd should take place after the afternoon or evening milking while cows are less socially active. Accustoming heifers to the milking parlour prior to calving has also been shown to encourage milk production by reducing their fear of the new surroundings. Although separating the calf within 24 hours of birth is less stressful and easier to manage, there is evidence that heifers which are allowed to suckle their calves for eight weeks experience a close to complete milk let down, improving whole lactation yields. 3:10/

10 Summary Because heifer rearing can be a significant drain on resources, each herd needs to examine its current replacement policy and realistic alternatives carefully for best overall value Heifer weight rather than age determines when puberty occurs and oestrus cycling begins The key to successful heifer rearing for two year calving is to maximise weight gains without creating over-fat animals Frame size assessed by height at the withers is perhaps the most valuable measure of heifer growth Heifer growth rates should be planned and monitored throughout the rearing period to achieve the required targets Accelerated calf growth systems, feeding as high a level of high protein milk replacer as calves can safely utilise, have been shown to give much heavier heifers at weaning and better development of udder secretory tissue Where rapid calf growth is required there may be a value in increasing the protein content in the calf starter concentrates above the 18% which has been shown to be optimal under conventional rearing systems Since fertility increases up to the third oestrus cycle after puberty, heifers need to be grown to reach puberty at least six weeks before the start of serving Growth rates of kg/day are recommended during the first pregnancy to achieve a Condition Score of 3.0 at calving, the key being to avoid heifers getting over-fat A bull fertility check is an essential investment in view of numerous cases of infertile bulls running with heifers Oestrus manipulation programmes have a valuable role for heifers Introducing heifers into the herd needs careful handling to minimise production and fertility-compromising stresses. Section 6: Managing Heat Detection See also Section 7: Optimising Herd Nutrition Section 8: Addressing Herd Management Section 11: Fact Sheet 10: Avoiding Calving Difficulties Fact Sheet 12: Herd Replacement Systems :10/07